Starting in 2012, California and other states will require all HVAC systems of at least six tons capacity having two or more refrigeration stages to reduce blower speed by 33% when operated at part-load cooling. In response, various manufacturers have set about designing new HVAC systems, such as rooftop units (RTUs) capable of complying with these new, “two-speed”regulations.
Complying with the regulations is not a straightforward issue. One of the key items impacted by blower speed is the amount of fresh air that the HVAC system provides. Customers are left with an unfortunate choice: either operate the blower at high speed and over-ventilate, or operate the blower at low speed and under-ventilate. Neither solution is acceptable. The former yields high energy costs; the latter runs afoul of building ventilation codes.
Another key concern is that, while blower speed can be reduced when the HVAC system is cooling, the same can be quite harmful when the HVAC system is heating. Reducing blower speed when the HVAC system is in a heating mode reduces heat exchanger airflow, causing system shutdowns dues to overheating and premature heat exchange failures.
As stated above, various manufacturers are designing new HVAC systems to accommodate multi-speed blower operation and comply with the two-speed regulations. However, the new systems are designed from the ground up using (e.g., microprocessor-based) direct digital controls (DDCs) to accommodate the many modes in which the HVAC systems should operate. An overwhelming number of today's HVAC systems, including the huge installed base of existing HVAC systems in service all over the world, lack DDCs and are therefore distinctly disadvantaged in trying to comply—simply reducing blower speed unacceptably disrupts their operation. To add to the problems, HVAC system manufacturers are unsure that they can justify offering HVAC systems designed to comply with regulations in place in only a few states; customers in states that have not adopted them are likely to refuse to pay additional money to achieve unnecessary compliance.